When not using TEXTURE_RECT path, flips have to sent via another method to the shader, to ensure that normal maps are correctly adjusted for direction. This PR adds an extra vertex attribute, LIGHT_ANGLE.
For nvidia workarounds, where the shader still has access to the final transform and extra matrix, the LIGHT_ANGLE can be 0 (no adjustment), 180 degrees for a horizontal flip, and negative indicates a vertical flip.
For batching path, the LIGHT_ANGLE can be used to directly specify the light angle for normal mapping, even when the final transform and extra matrix have been baked into vertex positions, so the same shader can be used for both.
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